discovered and conserved C. arabica accessions, nearly 34% C. arabica genotypes
are of low caffeine varieties. The caffeine contents in the C. arabica coffee varieties
vary from 0.62% to 1.82% [74]. Nevertheless, interspecific grafting in C. arabica
did not show expected results, but this vast genetic diversity in C. arabica with
respect to caffeine contents provides a strong basis for intraspecific grafting and
hybridization within in the C. arabica varieties. Still there is no study available about
the intraspecific grafting intending to generate the low caffeine C. arabica hybrid
varieties. Generation of caffeine free or low coffee varieties is also a way of
improving the existing cup quality, organoleptic traits, and physical characteristics
of C. arabica coffee since caffeine and chlorogenic acid involve in enhancing the
bitterness, acidity of liquor, and smaller size green beans [71, 74]. Caffeine is found
in a composite form with chlorogenic acid [75], but the quantity of chlorogenic acid
in different varieties was found to be in a close proximity while caffeine’s amount
varies significantly exhibiting that only a fraction of chlorogenic acid is in complex
with caffeine [76]. Chlorogenic acid made three quinic acid ester groups with caffeic
acid, namely, caffeoylquinic acids (CQA) and dicaffeoylquinic acids (diCQA)] or
with ferulic acid feruloylquinic acids (FQA) [24]. Each group has three isomers with
5-CQA being the amplest isomer. Caffeine production is a 94% genetic trait [77], but
still the variation of caffeine among coffee varieties cannot be explained by the
absence or presence of the governing gene [76]. The quantitative trait loci (QTL)
coupled with principal component analysis (PCA) approached identified two independent locus CQAL and RCQL located on two linkage groups responsible for the
variation of caffeine among coffee varieties. The level of caffeine enhances with
level of CQAt (total CQA), but relationship between caffeine/CQAt is not absolute
in all coffee varieties, suggesting that RCQL would regulate the ratios of caffeine
and CQAt [75]. The QTLs involved in the yield and technological traits related to
quality were also first time identified in the subgroups of pseudo-backcross individuals of C. robusta (Guinean 410 Â Congolese A03): seven QTLs for yield, six QTLs
for rate of pea berries, eleven QTLs for bean size, eight QTLs for 3-CQA and 4CQA, and one QTL zone for each; caffeine and trigonelline, 5-CQA and bitterness
were detected. For acidity and bitterness, male and female additive effect was also
found. Up to 15% variability was detected in the QTLs for the organoleptic traits
except 54.8% for acidity [78]. The detection of QTLs for organoleptic properties is a
milestone for it can be used as an indirect way to improve these traits in the different
varieties and used in the development of genetic maps to study the relative order of
genetic markers and their relative distances for finally underway genome sequencing
projects of coffee. A complete genetic linkage map for C. robusta and a partial
linkage map of (C. pseudozanguebariae X C. liberica) are also reported and
available [75]. Besides the development of cultivars with imparted desired biochemical composition, the cultivars with conferred preharvesting quality attributes are
also crucial for safety and maintaining the quality parameters of coffee berries till
before the start of harvesting. The different cultivars are developed for different
cultivation systems. For conventional cultivations systems, large and tall tree cultivars (e.g., Mundo Novo) and for denser to super denser systems medium to small
size cultivars with compact, cylindrical, or erect canopy (e.g., Catuai), for better
656
A. Hameed et al.
are of low caffeine varieties. The caffeine contents in the C. arabica coffee varieties
vary from 0.62% to 1.82% [74]. Nevertheless, interspecific grafting in C. arabica
did not show expected results, but this vast genetic diversity in C. arabica with
respect to caffeine contents provides a strong basis for intraspecific grafting and
hybridization within in the C. arabica varieties. Still there is no study available about
the intraspecific grafting intending to generate the low caffeine C. arabica hybrid
varieties. Generation of caffeine free or low coffee varieties is also a way of
improving the existing cup quality, organoleptic traits, and physical characteristics
of C. arabica coffee since caffeine and chlorogenic acid involve in enhancing the
bitterness, acidity of liquor, and smaller size green beans [71, 74]. Caffeine is found
in a composite form with chlorogenic acid [75], but the quantity of chlorogenic acid
in different varieties was found to be in a close proximity while caffeine’s amount
varies significantly exhibiting that only a fraction of chlorogenic acid is in complex
with caffeine [76]. Chlorogenic acid made three quinic acid ester groups with caffeic
acid, namely, caffeoylquinic acids (CQA) and dicaffeoylquinic acids (diCQA)] or
with ferulic acid feruloylquinic acids (FQA) [24]. Each group has three isomers with
5-CQA being the amplest isomer. Caffeine production is a 94% genetic trait [77], but
still the variation of caffeine among coffee varieties cannot be explained by the
absence or presence of the governing gene [76]. The quantitative trait loci (QTL)
coupled with principal component analysis (PCA) approached identified two independent locus CQAL and RCQL located on two linkage groups responsible for the
variation of caffeine among coffee varieties. The level of caffeine enhances with
level of CQAt (total CQA), but relationship between caffeine/CQAt is not absolute
in all coffee varieties, suggesting that RCQL would regulate the ratios of caffeine
and CQAt [75]. The QTLs involved in the yield and technological traits related to
quality were also first time identified in the subgroups of pseudo-backcross individuals of C. robusta (Guinean 410 Â Congolese A03): seven QTLs for yield, six QTLs
for rate of pea berries, eleven QTLs for bean size, eight QTLs for 3-CQA and 4CQA, and one QTL zone for each; caffeine and trigonelline, 5-CQA and bitterness
were detected. For acidity and bitterness, male and female additive effect was also
found. Up to 15% variability was detected in the QTLs for the organoleptic traits
except 54.8% for acidity [78]. The detection of QTLs for organoleptic properties is a
milestone for it can be used as an indirect way to improve these traits in the different
varieties and used in the development of genetic maps to study the relative order of
genetic markers and their relative distances for finally underway genome sequencing
projects of coffee. A complete genetic linkage map for C. robusta and a partial
linkage map of (C. pseudozanguebariae X C. liberica) are also reported and
available [75]. Besides the development of cultivars with imparted desired biochemical composition, the cultivars with conferred preharvesting quality attributes are
also crucial for safety and maintaining the quality parameters of coffee berries till
before the start of harvesting. The different cultivars are developed for different
cultivation systems. For conventional cultivations systems, large and tall tree cultivars (e.g., Mundo Novo) and for denser to super denser systems medium to small
size cultivars with compact, cylindrical, or erect canopy (e.g., Catuai), for better
656
A. Hameed et al.